As devices for inspecting a foreign substance on a semiconductor wafer, a defect of a circuit pattern thereof, etc., devices using electron beams are being used. In these electron beam inspection devices, a scanning electron microscope in which an electron beam is focused in the shape of a point and is scanned has become mainstream. In order that the electron beam inspection device perform inspection with desired resolution and sensitivity while suppressing damages to an observed sample, the irradiation energy of the electron beam is controlled by applying a voltage to the semiconductor wafer. Application of this voltage is called retarding. Although an electric field arises above the sample by the retarding, this electric field is not uniform near a sample edge and is distorted. As a result, a trajectory of the electron beam is bent irregularly, and consequently beam shift, shading, etc. occur; therefore, it is difficult to observe a correct image at the sample edge. Any device that uses the retarding with the use of the charged particle beam has a possibility that an effect caused by such disturbance of the electric field may occur.
An inspection device called a projection type inspection device is known from Japanese Unexamined Patent Application Publication No. H11 (1999)-108864, etc. as a kind of observation technique whereby a retarding voltage is applied to the sample and observation is performed using the electron beam. This technique is one that irradiates the electron beam as an “area beam” having a two-dimensional spread instead of scanning the electron beam as a “point beam” in order to increase the inspection speed higher than that of a technique using the scanning electron beam. The negative retarding voltage that has almost the same absolute value as that of an acceleration voltage is applied to the sample and its trajectory is inverted immediately before the electron beam being irradiated to the sample collides against the sample. The irradiation electron beam is inverted with respect to the trajectory on an equipotential plane formed above the sample by the retarding voltage, and a contrast that depends on a gradient of this equipotential plane is formed as an image. This technique is very excellent in sensitivity to the gradient of the equipotential plane, but on the other hand, causes a large beam shift due to distortion of the equipotential plane at the sample edge, which makes it difficult to acquire the image.
As a method of making uniform the electric field generated above the sample by the retarding over the whole sample surface and thereby lowering the disturbance of the image, a method of installing an electrode for making the electric field in the sample peripheral part uniform is proposed in Japanese Unexamined Patent Application Publication No. 2000-149845. This method is one in which a conductor plate almost as high as a sample surface is disposed in the sample peripheral part above the sample holder leaving a minute gap to the sample and the conductor plate is brought into electrical conduction with the sample holder.
In addition, other methods are described in Japanese Unexamined Patent Application Publication No. 2004-235149 and Japanese Unexamined Patent Application Publication No. 2004-14251. In each of these methods, a conductor plate that is electrically isolated from the sample holder with an insulator is provided above the sample holder of the sample peripheral part. The conductor plate is connected to a power supply other than the power supply for supplying the retarding voltage and suppresses the disturbance of the electric field above the sample by applying an arbitrary voltage to the conductor plate.